Examples of a device for optically reading a document include a copying machine and a scanner. Examples of a method of reading the document using these apparatuses include a pressure plate method using a document reading unit and a method using a sheet through document feeder (ADF).
FIG. 18 is a diagram typically showing a reading mechanism for a general document reading unit. In the pressure plate method, a document 11 to be read is put on a contact glass 12. A carriage 15 including an illumination lamp 13 and a mirror group 14 is moved with respect to the document 11. Consequently, a document surface is read. The carriage 15 is driven by means of a stepping motor which is not shown.
On the other hand, in the pressure plate method, the moving speed of the carriage 15 for the document 11 is controlled when reading the document. Consequently, the number of optical reading lines per unit distance is controlled in the moving direction of the carriage 15 (which will be hereinafter referred to as a feeding direction).
More specifically, when the original document 11 is to be enlarged, the carriage 15 is controlled to be moved more slowly than when the ratio of the size of the original document 11 to that of the output document is 1:1. When the carriage 15 is moved slowly, the number of the reading lines per unit distance in the feeding direction is increased.
On the contrary, when the document 11 is to be reduced (contracted), the carriage 15 is controlled to be moved quickly. When the carriage 15 is moved quickly, the number of the reading lines in the feeding direction is decreased. Thus, the enlargement/reduction processing in the feeding direction is carried out. On the other hand, one line data are electrically subjected to the enlargement/reduction processing to carry out the enlargement or reduction in a direction crossing the feeding direction (which will be hereinafter referred to as a scanning direction).
In general, a copying machine is provided with a document size sensor which detects the document size electrically. The size of the document is detected with this document size sensor before the movement of the carriage 15 is started, that is, before starting the rearing of the document 11. Accordingly, if enlargement/reduction is selected, before starting the rearing of the document, the amount of enlargement/reduction is calculated based on the document size and the paper size.
For example, even if documents having variable sizes such as A3, B4, A4 or B5 are put on the contact glass 12 in a longitudinal or transverse direction, a parameter for enlargement/reduction control is calculated by a process controller before the movement of the carriage 15 is started. The moving speed of the carriage 15 is controlled based on the parameter.
FIG. 19 is a diagram typically showing a reading mechanism using an ordinary sheet through document feeder. The document 11 to be read is delivered to automatically pass through a reading position by means of a sheet through document feeder 16 having a document feeding mechanism.
The carriage 15 is maintained to be fixed into the reading position. In other words, in the pressure plate method, the carriage 15 is moved with respect to the stationary document 11. However, when the sheet through document feeder 16 is used, the document 11 is moved with respect to the stationary carriage 15.
The moving speed of the document 11 is controlled by the driving operation of the stepping motor (which is not shown). The moving speed of the document 11 is controlled when the document 11 is to be enlarged or reduced in the document feeding direction. In the same manner as in the pressure plate method, the enlargement or reduction can be implemented by changing a relative speed for the movement between the document 11 and the carriage 15.
When the sheet through document feeder 16 is used, the size of the document is detected by means of a mechanical sensor. The size of the document in the feeding direction is detected when the operation for reading the document 11 is completed. In other words, the size of the document 11 in the feeding direction is unknown when starting reading of the document 11. Accordingly, it is impossible to calculate a parameter for enlargement/reduction control. For this reason, the feeding speed of the document 11 cannot be controlled depending upon the enlargement/reduction factor.
Along the scanning direction, the document size is detected when the document 11 reaches the position of a sensor. Accordingly, when the documents 11 of various sizes exist, it is impossible to calculate the parameter for the enlargement/reduction control before the document reading processing is started.
The image of the document 11 which is read by using the sheet through document feeder 16 has a mirror image relationship with an image obtained in a pressure plate mode in the scanning direction. Accordingly, a mirroring processing of replacing the right with the left is carried out during image output.
These days a digital copying machine has come into market in addition to the analog copying machine. The digital copying machine has such a structure that a paper document or the like is optically read and a read image signal is converted into a digital image signal to carry out an image processing. In the digital copying machine, moreover, there has been a digital composite machine having a scanner function, a printer function and a facsimile function in addition to a copying function.
Some digital copying machines and some digital composite machines (which will be hereinafter referred to as a digital composite machine and the like) carry out enlargement/reduction through electrical control in place of the enlargement/reduction through mechanical control described above.
For example, Japanese Patent No. 2789560 discloses a “enlargement/reduction processing apparatus for image data” as an example of such a machine. Further, Japanese Laid-Open Patent Publication No. HEI 8-274986 discloses “image processing apparatus” as an example of a digital composite machine.
In a conventional document reading mechanism using the sheet through document feeder, however, there has not been proposed an apparatus capable of automatically copying documents having various sizes with an enlargement or a reduction. The reason is that the conventional document reading mechanism cannot discriminate the size of the document before the document is started to be read. Thus, size after enlargement/reduction cannot be determined.